Basic Trauma Course Mechanism of Injury

Mechanism of Injury Mechanism of injury (MOI) can be defined as an exchange of forces that results in an injury to a person. Mechanism of injury more accurately describes both the force and subsequent tissue response. The actual injury occurs when the force deforms tissues beyond their respective abilities to compensate, absorb, or diffuse the energy. . Sir Isaac Newton's Law of Inertia is probably the most important concept: 'A body in motion will remain in motion unless acted upon by an outside force'. Law of Conservation of Energy, which states: Energy can neither be created or destroyed. It is only changed from one form to another. Whenever we speak of trauma, it is necessary to understand mechanism of injury. As much as we hate to admit it, physics plays an important role in MOI. This is best illustrated by the Motor Vehicle Crash, keeping in mind that it makes a big difference if the force is applying the brakes at a red light versus the car slamming into a tree. Obviously, the forces applied here leave drastically different outcomes. Think about the brakes and the tree again. The brakes are designed to absorb the inertial forces, the tree was not. In the case of the tree, which was not put there to stop a car, it is the car as a whole that must deal with all that energy, hence the damage to the car instead of the tree. MOI includes how the injury occurred, the circumstances surrounding the injury (why), where the injury occurred (considering not only the part of the body, but also the geographic location and description of the surface impacted), when the injury occurred (remember the 'Golden Hour'), as well as who was injured. Each bit of this information assists the health care team to put together the events and determine various injuries and their potential impact on the individual.

Kinetic Energy Kinetic energy is dependent upon an object’s mass and its velocity (speed). As speed increases, kinetic energy increases exponentially. When an impact occurs and the energy is transferred to another object, the energy is described as a force. The most common forces encountered in traumatic injury are Acceleration, Deceleration, and Shear forces. A car traveling 20 miles per hour will cause four times the damage than the same car traveling at 10 miles per hour. Acceleration is the change in rate of velocity (speed) of a moving body; as velocity increases, so does tissue damage. Deceleration describes a decrease in the velocity of a moving object. Shear forces occur across a plane, with structures slipping relative to each other (most commonly the brain slipping along the base of the skull). Many people mistakenly presume that it is the impact of the car into the tree that causes the injuries. In actuality, each Motor Vehicle Crash includes three separate impacts. These are: Auto vs. another object. Machine Collision Occupant body vs. interior of auto or seat belt. Body Collision Internal tissues/organs vs. rigid body surfaces (bones). Organ Collision

Typical Patterns of Injury MVC Motor cycle crash Auto versus pedestrian Explosive blast injuries Falls from significant heights Page 14-15 Tables 2-3, 2-4, 2-5

What questions do we ask? Vehicle Collisions Type of crash Location in the vehicle Type of seat belt worn (Lap belt vs. three point restraints) Presence and deployment of airbags (frontal, side impact) Whether a helmet was worn (Motorcycle or bicycle) Speed of vehicle at impact Whether rapid deceleration occurred What was hit Interior and exterior damage to the vehicle, including a spider type configuration on the windshield from the inside Intrusion into the passenger compartment of the vehicle Whether the patient hit the steering wheel, dashboard, or windshield Condition of steering wheel, dashboard (bent, indented), and windshield Evidence of vehicle rollover, and if so, approximately how many times. These questions may be answered by the patient, by EMS providers, patient families, or law enforcement.

What questions do we ask? Gunshot wounds or stabbings Type of weapon (Type of knife or firearm) Caliber of bullet Length of knife Position of patient when event occurred Falls Height of fall What the patient landed on Impacted body parts